Alien Seas: Oceans in Space

By Michael Carroll and Rosaly Lopes

Oceans were long thought to exist in all corners of the Solar System, from carbonated seas percolating beneath the clouds of Venus to features on the Moon's surface given names such as "the Bay of Rainbows” and the "Ocean of Storms." With the advent of modern telescopes and spacecraft exploration these ancient concepts of planetary seas have, for the most part, evaporated. But they have been replaced by the reality of something even more exotic. For example, although it is still uncertain whether Mars ever had actual oceans, it now seems that a web of waterways did indeed at one time spread across its surface.

The "water" in many places in our Solar System is a poisoned brew mixed with ammonia or methane. Even that found on Jupiter's watery satellite Europa is believed similar to battery acid. Beyond the Galilean satellites may lie even more "alien oceans." Saturn's planet-sized moon Titan seems to be subject to methane or ethane rainfall. This creates methane pools that, in turn, become vast lakes and, perhaps, seasonal oceans. Titan has other seas in a sense, as large shifting areas of sand covering vast plains have been discovered. Mars also has these sand seas, and Venus may as well, along with oceans of frozen lava. Do super-chilled concoctions of ammonia, liquid nitrogen, and water percolate beneath the surfaces of Enceladus and Triton? For now we can only guess at the possibilities.

'Alien Seas' serves up part history, part current research, and part theory as it offers a rich buffet of "seas" on other worlds. It is organized by location and by the material of which various oceans consist, with guest authors penning specific chapters. Each chapter features new original art depicting alien seas, as well as the latest ground-based and spacecraft images. Original diagrams presents details of planetary oceans and related processes.

• Language: English
• Publisher: Springer
• Release date: Jul 19, 2013
• ISBN: 9781461474739

Book preview

Michael Carroll and Rosaly Lopes (eds.)Alien Seas2013Oceans in Space10.1007/978-1-4614-7473-9_1

© Springer Science+Business Media New York 2013

1. Introduction: Oceans on Earth and Elsewhere

Michael Carroll¹  

(1)

Littleton, CO, USA

Michael Carroll

Email: [e-mail]

Abstract

Samuel Taylor Coleridge’s ancient mariner lamented, Water, water, everywhere, nor any drop to drink. Today, it seems that planetary scientists are faced with the same situation. Drinking aside, the prospect of oceanic planets and moons scattered across the cosmos is brighter than ever. During its first 3 years of operation, NASA’s planet-hunting Kepler spacecraft tracked down somewhere in the neighborhood of 100 planet candidates that appear to be in the habitable zone around their parent stars. In other words, these planets, or moons circling planets in the case of giant planets, have the capacity to support liquid water on their surfaces.

Samuel Taylor Coleridge’s ancient mariner lamented, Water, water, everywhere, nor any drop to drink. Today, it seems that planetary scientists are faced with the same situation. Drinking aside, the prospect of oceanic planets and moons scattered across the cosmos is brighter than ever. During its first 3 years of operation, NASA’s planet-hunting Kepler spacecraft tracked down somewhere in the neighborhood of 100 planet candidates that appear to be in the habitable zone around their parent stars. In other words, these planets, or moons circling planets in the case of giant planets, have the capacity to support liquid water on their surfaces.

With some 2,300 candidate planets beyond our own solar system, and counting, these pages cannot hope to cover all that cosmic territory. But seas in many forms await our studies within our home planetary system. There are oceans of water beyond the Earth, below the icy crusts of satellites in the outer solar system. Surface oceans probably existed on Mars in the past, and perhaps on Venus as well. Saturn’s planet-sized moon Titan hosts respectable seas of liquid methane or ethane. Truly alien oceans of liquid metallic hydrogen slosh at the heart of outer planets, while seas of sand cast gritty tides across frozen landscapes of ice and rock in other places.

A Short History

Oceans have played an important role in humanity’s story, and it’s been a tumultuous relationship. Ancient peoples often feared the briny unknown. Many ancients believed that a mysterious, monster-filled ocean surrounded the world. Most ships built in the fertile crescent were not safe on the open seas, as they were designed for travel on rivers or across floodplains. Roman law simply forbade sea travel between November 10 and March 10, as the period was considered too risky. As vessels became more seaworthy and explorers began to venture further into the great oceans, their maps reflected their unease with labels like Thar Be Dragons and Zona Incognita.

Nevertheless, early explorers ventured great distances into the unknown. Asian populations spread through Polynesia and Micronesia. The Vikings set up shop in Iceland and visited several sites in North America. It is possible that many early humans migrated from Siberia to the western hemisphere traveling by small boats, staying close to shore. Some 1,600 years before Christ, the Minoans set sail across the Mediterranean in the largest flotilla of the ancient world, waging war not with weapons but with economics and trade. In fact, ancient Egyptian texts—typically disdainful of foreigners—assigned the Minoans the respectful label the Sea Peoples.

Though they may at times be terrifying, the Earth’s oceans are crucial to life and are thought to be where primitive life originated. The oceans have a profound influence on climate, enabling life to exist in some regions, while sometimes causing havoc in others. Oceanic currents transfer heat from the tropics to polar regions, helping to drive our weather. Changes in currents, such as the famous El Nino effect, cause seasonal shifts in wind, rain and temperature patterns globally. Our oceans play a critical role in climate stability and in the carbon cycle, providing an interface between atmosphere and surface.

But what of seas in the sky? What about seas on the orbs floating in those fuzzy telescopic views? Even through the eyepiece, the Moon’s dark plains looked like bays, ponds and seas. Hence, many are named Maria (sea), Lacus (lake), Palus (marsh), and Sinus (bay). Jules Verne sent his cannon-shell-riding passengers around the far side of the Moon while it was in darkness, conveniently. When meteors briefly lit the landscape below, they got a tantalizing glimpse. Could they see rivers? Forested hillsides? Seas? Nearly a century later, Ray Bradbury gave us his chess-piece civilizations in the Martian Chronicles, where we saw a Mars with wine-colored canals and slumbering fossil seas.

Science Leaps In

Early astronomers added their voices to the literary crowd. The first telescopic observations of Venus frustrated efforts to determine its length of day or the nature of its landscape; what became obvious was that the world was covered in hazes and clouds. Venus is the closest planet to the Earth, and virtually identical in size, leading some observers to guess that the Venusian landscape might be Earthlike: swamp-covered or blanketed in oceans of carbonated water, a planetary Perrier source. Spacecraft laid waste to this Venus version, but have provided some evidence of possible ancient oceans.

While some astronomers looked sunward toward Venus, others cast their gaze outward, in the direction of Mars. Antoniadi, Schiaparelli, and a host of others saw the Martian resemblance to Earth right away. They clocked its days at about 24 h and 40 min. They found a season-producing axial tilt similar to our own, and noted the ebb and flow of its polar ices. Meticulously, observers mapped the wave of darkening spreading across the mysterious web of shapes draping the face of the red planet. Rich Bostonian diplomat Percival Lowell set up his own observatory to study the strange world, crafting intricate, canal-filled maps. Reasoning that Mars’ apparently straight lines seemed more artificial than natural, Lowell proposed that these dark canals sprang from an artificial source, engineered by what he postulated as a dying, advanced race holding on the last vestiges of long-dead seas. Early observers also guessed that the outer planets might be oceanic, great globes of liquid sloshing under bands of clouds. They were surprisingly close to the truth.

Alien Seas

Alien Seas explores the wonders of distant seas across our solar system. Late-breaking research brings us vistas of seascapes that no one even dreamed of until a few decades ago. Armed with spacecraft data, advanced ground observation tools, and powerful new computer models, researchers are revealing strange, new worlds brimming with truly alien seas.

In our first chapter, NASA astrobiologist David Grinspoon introduces us to the alien seas that may once have lapped against the shores of ancient Venus. In Chap.​ 2, JPL’s Timothy Parker takes us to Mars, where past epochs have left the fingerprints of flood plains, river valleys, and perhaps telltale evidence of beaches lining vast oceans of acidic water. JPL volcanologist Rosaly Lopes takes us farther back in time, where we witness pelagic expanses of lava that covered planets and moons in their formative years. In Chap.​ 4, more familiar seas of water may meet us within three moons of Jupiter. Robert Pappalardo, also from JPL, tours Europa, Ganymede and Callisto. The Southwest Research Institute’s John Spencer delves into the oceans of ice and water blanketing the outer moons, with a focus on Saturn’s dramatic erupting satellite Enceladus. Jani Radebaugh of Brigham Young University journeys to a different kind of ocean: seas of sand. Her sixth chapter provides an overview of the bizarre dunes on Venus, Mars and Titan. Titan is also blessed with seas of liquid ethane, as JPL’s Karl L. Mitchell shows us in Chap.​ 7. Kevin Baines (JPL/ University of Wisconsin-Madison) and chemist Mona Delitsky (California Specialty Engineering) team up to go deep in Chap.​ 8, investigating the hearts of the gas and ice giants, where dense air becomes alien oceans of liquid metallic gases. NASA/Ames’ astrobiologist Chris McKay takes a look at Earth’s exotic life, and how it might shed light on the possibilities of life in distant oceans. Finally, astrophysicist Jeffrey Bennett rounds out our cosmic sea inventory by honing in on exoplanets near and far, where familiar seas may lap the shores of moons circling gas giants orbiting close to their suns. Join us as we explore alien seas!

Michael Carroll and Rosaly Lopes (eds.)Alien Seas2013Oceans in Space10.1007/978-1-4614-7473-9_2

© Springer Science+Business Media New York 2013

2. Chasing the Lost Oceans of Venus

David Grinspoon¹  

(1)

Denver Museum of Nature and Science, Denver, CO, USA

David Grinspoon

Email: [e-mail]

Abstract

NASA astrobiologist David Grinspoon introduces us to the alien seas that may once have washed across the shores of ancient Venus. Orbiting spacecraft have detected high amounts of chemicals pointing to vast amounts of water in the Venusian past. Earth’s sister world may have harbored a host of lakes and seas.

Is it deranged to build a good part of a career studying something that may or may not have been? I study the oceans of Venus. Maybe it’s the scientific equivalent of an artist who emphasizes negative space—focusing on something that is believed to have existed but is no longer there. And yet I believe. True confession: I’ve even dreamed about them (Fig. 2.1).

A216957_1_En_2_Fig1_HTML.jpg

Fig. 2.1

A primordial ocean washes across a battered crater rim, as volcanoes in the distance strive to dominate what will eventually become their realm. Any early seas on Venus would have eventually become acidic, boiling into a carbon dioxide sky. The continent of Ishtar Terra rises at left (Painting ©Michael Carroll)

I imagine them timeless, vast and deep, covering most of the planet except where mountains—conical volcanoes and steep rims of giant craters—jut skyward. I picture foaming waves lapping the eroding shores of those scattered highlands, blowing in warm breezes, sometimes raging into terrible storms but completely untroubled by tides.

There’s no moon to raise the tides and perhaps no early trauma of a moon-forming collision,¹ without which—all else being equal²—Venus may have retained more water but left more of it buried in its less-distressed mantle.

Call me crazy. I’ve studied them my whole adult life and yet I’ve never seen them. Maybe I’m better off than a particle physicist who spends her life chasing some strange, charmed anti-gluon that turns out to not even have been a good idea. Or perhaps not much more pathetic than a geophysicist who focuses on Earth’s core that nobody has ever seen except in a couple of Hollywood mistakes. But, at least indirectly, we know the core is there. It gives its lurking presence away, like a fetus in the womb, in the attenuation patterns of seismic waves, which allow us to see the core. We can sense its presence indirectly in the Earth’s gravitational and magnetic fields.

I would argue that in a similarly indirect sense we can also sense the oceans of Venus. Only it’s worse because they are long gone, like the scientists on all those tissue-sample TV shows, we are seeking forensic evidence that is mostly vanished from the scene (Fig. 2.2).

A216957_1_En_2_Fig2_HTML.jpg

Fig. 2.2

The restless surface of Venus has obliterated geological records of ancient seas. (top) Tectonic faults and uplifted crust blanket Ovda Regio, whose surface may be only a few 100 millions years old geologically. (below) Volcanic mountains, lava flows, and associated fractures cover nearly 90 % of the Venusian surface (Magellan photos courtesy NASA/JPL)

I have friends who study extinct creatures or disappeared civilizations, but they can go and dig up evidence without risking instant death in 900° superpressurized air. In fact we simply can’t go look for ourselves³ so we have to send machines, and we haven’t been able to send very many, though not for lack of trying.

So we don’t yet know, but in the meantime we’ve been able to gather some pretty strong circumstantial evidence. The data are still loose enough to allow for a contrarian Venus was always dry opinion, but most scientists who have looked at all the evidence and how it fits into what we’ve learned about the entire solar system believe that almost surely Venus started out as a watery, more Earthlike place—a planet with warm, liquid water oceans (Fig. 2.3).

A216957_1_En_2_Fig3_HTML.jpg

Fig. 2.3

Infrared studies of Venus’ highland plateaus have detected the kind of heat signature often associated with granite. Granitic rock on Earth forms in the presence of plate tectonics and oceans. Left: Ridges and lava flows cut across Lavinia Regio. Right: The highland area Alpha Regio is 1,300 km across (Courtesy NASA/JPL/Magellan project)

What were they like? I see them alternately dappled with sunlight and dulled with thick cloud. When the sun does break through it is much closer than on Earth and therefore looks huge, twice as large as what we are used to. But it is also unnaturally pale as the young sun was markedly dimmer. When the clouds scatter, the full sun is 40 % less bright than what we see on Earth today.

That dim Sun⁴ is the reason why young Venus, despite her proximity to our star, should have been able to host oceans for eons. Stars like ours start out cooler. As they age, they fuse Hydrogen into Helium, and they gradually brighten. At some point, and we don’t yet know when, the warming sun crossed a threshold so that Venus could no longer hold her oceans. More sunlight heated the surface waters, causing evaporation, which fed water vapor into the air. Water vapor is itself a strong greenhouse gas, so this caused young Venus to heat up further, which caused still more evaporation, and so on. Evaporation causes more greenhouse heating causes more evaporation. A positive feedback. Thus was initiated the runaway greenhouse.

Runaway here refers to the fact that such a feedback loop is unstoppable. Once it started, the fate of those oceans would have been sealed. But it also applies in its other sense, for those oceans did run away—left home for good. When in the form of an ocean, water is gathered tight to a planet and largely protected from solar radiation. But once it enters the air as steam it is vulnerable to the sun’s ultraviolet, and the H2O is split.

The hydrogen drifts off into space and the oxygen chases after it or stays behind to react with minerals, forming rusty rocks and leaving Venus an empty nest, permanently stripped of its potentially life-giving waters.

We don’t know when this departure occurred, or how long it took, but we’re pretty sure it did happen. Today Venus is drier than Arizona in June. Much. It is ridiculously parched. The tiny trace of water vapor left in the air is about 100,000 times less than the water found on Earth’s surface. (although we don’t know how much water is trapped inside Earth’s interior and even less about any water trapped inside Venus…)

And we see convincing evidence of the watery exodus: like the shoes of refugees forced to leave in a hurry, we see the signs of a thorough evacuation of hydrogen which left behind a strong residue of deuterium—the more massive variant of hydrogen which has a harder time packing up and leaving. The huge build-up of this heavy hydrogen tells us that most of the water has escaped. Not when, or how much, just most.

The loss of water completed an irreversible and dramatic shift in climate. Do not let this happen to your planet! Rocky water worlds like Earth have a built-in thermostat that regulates climate over the long run, keeping it in the range of liquid water (which we carbon-in-water creatures pretty much demand as a minimum condition of residency). If it gets too cold then volcanic CO2 builds up in the atmosphere, eventually warming the planet. If it gets too hot then the rate at which water dissolves CO2 and weathers silicate rock into carbonate rock increases, drawing down the CO2 content and cooling the planet. This mechanism has worked over the ages to keep Earth’s climate more or less in line. It probably functioned on Early Venus as well. But once the last surface water was lost to the brightening sun, there was no efficient way to make carbonate rocks swiftly enough to counter the runaway warming. At this point the thermostat of Venus broke completely and the thermometer pegged in the red zone- where it has remained ever since (Fig. 2.4).

A216957_1_En_2_Fig4_HTML.jpg

Fig. 2.4

Some researchers suggest that Venus has always been a desert

Reviews for Alien Seas

[steve_walker-348810 · Rating: 5 out of 5 stars]

This is a beautiful and accessible book about one of the current "hot" topics in planetary sciences.